HR: 09:40h
AN: T31D-07    [Abstracts]
TI: High Resolution Anisotropic Structure of the North American Upper Mantle From Inversion of Body and Surface Waveform Data
AU: * Marone, F
EM: federica@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, University of California, 215 McCone Hall, Berkeley, CA 94720 United States
AU: Gung, Y
EM: ycgung@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 106 Taiwan
AU: Romanowicz, B
EM: barbara@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, University of California, 215 McCone Hall, Berkeley, CA 94720 United States
AB: Seismic anisotropy provides insight into upper mantle structure as well as paleo and recent deformation processes. To date, our knowledge of the North American anisotropic structure arises mainly from global tomographic models or \textit{SKS} splitting studies which lack horizontal and vertical resolution respectively, and are limited to either radial or azimuthal anisotropy. Our goal is a new high resolution model for the North American upper mantle incorporating both radial and azimuthal anisotropy. We hope to achieve unprecedented lateral and depth resolution by improving both methodology and data coverage. We invert seismic long period waveform data in the framework of normal mode asymptotic theory (NACT). The resulting broad band sensitivity kernels allow us to exploit the information contained in long period seismograms for fundamental mode surface waves, overtones and body waves simultaneously. Until now, this approach has only been applied at the global scale. We have adapted the NACT algorithm for the regional case by implementing a lateral parametrization in terms of spherical splines on an inhomogeneous triangular grid of nodes, with the finest mesh for North America. Moreover, accurate crustal corrections are essential for the quality of high resolution regional tomographic studies, because they prevent the mapping of unresolved shallow features into the mantle structure. Going beyond the linear perturbation approximation, we split the correction into a linear and non-linear part. In this way, we can deal with the large lateral variations over a short distance observed in Moho topography more accurately. The inverted dataset consists of more than 100,000 high quality 3 component body, fundamental and overtone surface waveforms, recorded at broad band seismic stations in North America from teleseismic events and provides a fairly homogeneous path and azimuthal coverage. We use information from \textit{SKS} splitting measurements as additional constraints on our anisotropic model. While we focus here on the first step and present the radial anisotropic structure, we also show preliminary results from a model characterized by a more complete anisotropic parametrization. We discuss the prominent features of the anisotropic upper mantle structure beneath North America, in the light of unresolved geophysical questions such as the nature and strength of lithosphere/asthenosphere coupling, the depth extent of continental sub-regions and the relation of observed seismic anisotropy to present-day asthenospheric flow and/or past tectonic events recorded in the lithosphere.
DE: 8180 Tomography
DE: 9350 North America
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting